This invention relates to a network system, data transmitter-receiver (transceiver), and failure location/compensation method in such a small-scale communications system required to be robust and reliable for safety purposes as is provided in an automobile.
In general, a communications network consists of devices (stations or nodes) and transmission lines, and is physically or logically arranged in a topology selected typically from dedicated line, bus, star, ring and mesh. The dedicated line provides a one-to-one connectivity between two specific devices via a private line. The bus topology consists of a single wire or cable and a plurality of stations connected thereto. The ring topology has a medium formed in a closed loop or ring to which a plurality of stations are connected. The mesh topology is a complex of other topologies, in which each node typically has at least two links to other nodes. In a network for establishing connections among a limited number of specific devices such as a communications system for devices installed in an automobile, not only the dedicated line and the star topology, but also the bus topology for use in a CAN (control area network) communication or PGM tester, are employed as well as any hybrid topologies resulting from combination of the above basic topologies (see JP 2002-94535 A).
However, these conventional topologies intrinsically involve difficulty in identifying and locating a failure, such that one can hardly determine where the failure occurs, in a device or on a transmission line. Therefore, in a routine operation for dealing with such a failure, first, the device in trouble, if located, is stopped, and then any problem, if it turns out to be still left unresolved, is treated as a breakdown of the communications system as a whole, in most instances. For example, in a ring topology as in common use, if a transmission line that connects two nodes is found faulty, communication is cut off at the faulty spot. A special system for maintaining the communication may sometimes be provided, but it is generally difficult to identify the communications line under the faulty condition. In some network configurations such as in a star topology or in a bus topology, where each node is independent from one another, when a failure occurs on a transmission line that provides connectivity between two nodes, the nodes are forced to be isolated from the system so that the communication throughout the whole system is securely prevented from failing. However, in a case where the isolated node holds important information for the communications system, the whole system would suffer too much to maintain the communication functionality thereof. Under these circumstances, it is conceivable that a hybrid topology with redundancy could be adopted in order to improve the robustness and reliability of the network, but the transmission lines only made physically redundant would increase the difficulty of detecting a failure at a single spot, thus concealing the failure that should be addressed proactively. In addition, in a case where each node including data transmitter-receiver is provided with redundancy, the whole communications system would disadvantageously become so large, and increase tasks of developing software and hardware therefor, thereby causing costs to add up.
Therefore, the present invention is made to eliminate the above disadvantages and it is one exemplified object to provide a means for maintaining communication functionality of the whole system by locating a failure on a transmission line and compensating for the loss due to the failure.